1. Field of the Invention
The present invention relates to an aircraft and, in particular, concerns an unmanned vertical take-off or landing air vehicle that is gyroscopically stabilized during flights so as to enhance controllability of the flight operations of the vehicle.
2. Description of the Related Art
Unmanned air vehicles (UAV) are vehicles that provide tremendous utility in numerous applications. For example, UAV""s are commonly used by the military so as to provide mobile aerial observation platforms that allow for observation of ground sites at reduced risk to military personnel. The typical UAV used in military applications, and also in other more civilian-type applications, is comprised of an aircraft that has the general configuration of fixed wing aircrafts known in the art. In particular, the typical UAV that is used today has a fuselage with wings extending outward therefrom, control surfaces mounted on the wings, a rudder and an engine that propels the UAV in generally forward flight. Typically, these UAV""s are radio controlled such that an operator can control the flight of the UAV from a remote location. UAV""s of the prior art can thus be used for obtaining photographic reconnaissance images without the risks to a pilot inherent in actually physically piloting the plane. While these UAV""s of the prior art have considerable utility, there are still some shortcomings which limit the versatility of known prior art UAV""s.
In particular, the typical UAV takes off and lands like an ordinary airplane. In particular, for take-off, the typical prior art UAV travels over a runway until sufficient airflow is created over the wings of the UAV such that the UAV takes off and begins to fly. Similarly, upon landing, the UAV is directed towards a runway and is then landed on the runway in the same manner as manned airplanes. However, in many circumstances, the use of runways for UAV""s is impractical.
For example, for military applications, land-based runways are often unavailable adjacent the operational military zone or the available runways will be occupied by larger manned fixed-wing aircraft. Similarly, shipborne UAV""s are even further restricted in available runway space due to the fact that most military ships are not equipped with sufficient deck space to constitute a runway for a UAV. To address this particular problem, UAV""s are often forced to be launched with expensive catapult systems and then recaptured using expensive net systems which can result in damage to the UAV. While some types of military ships, such as aircraft carriers, may have the available deck space to operate UAV""s, this available deck space is typically in full use by larger manned aircraft.
A further difficulty with airplane-type UAV""s is that these vehicles are often insufficiently mobile to allow the UAV to operate effectively in confined airspace. in particular, it is often desirable to be able to move the UAV in a confined airspace, such as in an urban setting, at relatively low elevations. Airplane-type UAV""s often travel too fast in order to operate effectively in these types of environments.
To address some of these problems, vertical take-off or landing (VTOL) UAV""s have been developed in the prior art. For example, a helicopter-type UAV is one type of aircraft that can take off on limited available runway space and can maneuver in confined air spaces. While helicopter-type aircrafts solve some of the problems associated with fixed-wing UAV, the helicopter type UAV""s also have some problems. In particular, helicopters are characterized by a relatively slow forward speed as the angle of attack of the rotor blade is limited. Moreover, helicopter-type UAV""s often pose dangers to individuals upon landing due to the exposed propeller blade. This problem is accentuated in circumstances where the UAV is to be landed on confined moving surfaces, such as the surfaces of ships operating at sea.
Various other designs of VTOL UAV""s have been developed, however, each of the existing designs suffer from stability problems in flight or relatively slow forward operational speeds. One example of a VTOL UAV is provided by U.S. Pat. No. 5,419,513 to Fleming, Jr., et al. The UAV disclosed in Fleming has a torroidal fuselage with a rotor assembly that provides thrust in a direction that is generally perpendicular to the plane of the torroidal fuselage. A pair of flight control surfaces are located on the outer perimeter of the fuselage so as to provide stability during forward flight. While the UAV disclosed in this patent is capable of vertical take-off and landing, this UAV is likely to be unstable in flight and is also likely to be limited in its speed of forward flight for the same reasons that a helicopter is also limited in its speed of forward flight. In particular, the propellers cannot be oriented such that the plane of rotation of the propellers is perpendicular to the direction of travel of the aircraft and, consequently, the forward speed of the aircraft is thus limited. Moreover, with these types of designs, it will be appreciated that stability during flight is also difficult to achieve as the flight envelope of this type of aircraft is relatively finite.
The stability of these types of aircraft has been addressed, somewhat imperfectly, through the use of gyroscopic stabilization members that provide rotational inertia to the aircraft to stabilize the aircraft during flight. One example of such an aircraft is provided by U.S. Pat. No. 4,461,436 to Messina. In Messina, a flying saucer shaped body is disclosed as having a propeller and a gyroscope is added into the body of the aircraft wherein the gyroscope is induced to rotate as a result of airflow from the propeller. While the aircraft disclosed in the Messina patent may provide somewhat greater gyroscopic stability, this particular aircraft does not contemplate transitioning from vertical flight, with the plane of the propeller substantially parallel to the plane of the earth, to substantially horizontal flight where the plane of the propeller is substantially perpendicular to the plane of the earth. This transition is generally thought to have significant stability difficulties that are unlikely to be overcome by the addition of the airpowered gyroscope.
Yet another example of a VTOL aircraft that has some degree of gyroscopic stabilization is provided in U.S. Pat. No. 5,890,441. This particular patent discloses a very complex aircraft having multiple vertically directed and horizontally directed propellers to provide a combination of horizontal and vertical thrust to operate the aircraft. It is believed that the counter-rotation of these propellers are likely to limit the gyroscopic stabilization effect provided by the propellers thus leaving the aircraft more unstable in flight. Moreover, the use of multiple rotating propellers adds to both the cost and the complexity of the aircraft.
From the foregoing, it will be apparent that there is a need for a UAV aircraft that is capable of vertical takeoff or landing that is both inexpensive and stable in flight. Moreover, there is a need for a VTOL UAV that is capable of travelling not only in a slow hover mode but is stable enough to transition to substantially full horizontal flight for fast movement.
The aforementioned needs are satisfied by the unmanned air vehicle of the present invention which is comprised of a fuselage that defines aerodynamic flight surfaces, an engine mounted to the fuselage having an engine shaft arranged to rotate about a longitudinal axis with respect to the fuselage, and a propeller mounted to the engine shaft so as to rotate to thereby provide thrust so as to cause the UAV to travel through the air. The aircraft also comprises a gyroscopic stabilization member coupled to the shaft such that rotation of the engine shaft results in rotation of the gyroscopic member wherein the gyroscopic member is selected so as to have an angular momentum that is at least approximately 30 times larger than the moment of inertia of the aircraft so that the aircraft is gyroscopically stabilized throughout the entire flight envelope.
In one aspect, the aircraft includes a flight control system that is adapted to control the flight of the aircraft during the entire flight envelope. The control system is adapted to permit vertical take-off or landing of the vehicle with the plane of the propeller being substantially parallel to the plane of the ground through a transition to horizontal flight wherein the plane of the propeller is substantially perpendicular to the plane of the ground and wherein gyroscopic stabilization is provided during such transition.
The use of a gyroscopic stabilization member for such an aircraft means that the aircraft will be more stable during the entire flight envelope as the effects of external and internal moments, such as changes in moments. due to fuel consumption or wind gust, result in gyroscopic precession of the vehicle. As a result of the gyroscopic precession, the changes in direction of flight of the vehicle as a result of such internal or external moments occur 90 degrees in the direction of rotation from the point where the resulting moment is applied. Preferably, the angular momentum of the gyroscopic member is large enough such that possible variations of the vehicle orientation due to wind gust will be rapidly suppressed without affecting the air vehicle""s position in space.
In one particular environment, the gyroscopic member that rotates as a result of rotation of the engine shaft is comprised of a weighted disc that is coupled to the drive shaft via a gear assembly such that the disc can be rotated at an angular velocity selected to provided the gyroscopic stabilization for the air vehicle. In another embodiment, the gyroscopic stabilization member is comprised of a ring that is attached to the outer ends of the blades of the propeller and the ring is also selected so as to have a mass that will result in the gyroscopic stabilization member having a sufficient angular momentum so as to gyroscopically stabilize the aircraft. In yet another embodiment, the propeller itself is formed to have sufficient weight relative to the other components of the air vehicle such that the propeller gyroscopically stabilizes the vehicle.
In one particular aspect of the invention, the fuselage defines an opening extending therethrough, and a propeller and engine are mounted within the opening so as to provide a ducted fan configuration for the air vehicle. The gyroscopic stabilization member is mounted on the engine shaft so as to also be positioned within the opening defined by the fuselage. The flight control system includes a plurality of movable flight control surfaces that can be independently moved so as to provide directional control about a pitch, yaw and roll axes. In all orientation of flight, the gyroscopic stabilization member provides gyroscopic stabilization about the pitch and yaw axes of the vehicle. The flight control system is adapted to allow the ducted fan fuselage to take-off and land in a manner where the plane of rotation of the propeller is substantially parallel to the landing surface.
The ducted fan aircraft is further configured such that, following vertical take-off, the plane of the propeller can be oriented so as to be approximately 5-10 degrees offset from the plane of the earth so as to propel the vehicle in a direction parallel to the plane of the earth at a relatively low speed in a well-known manner. The flight control system is further configured so as to cause the ducted fan air vehicle to orient itself such that the plane of the propeller is substantially perpendicular to the plane of the earth to allow for more rapid horizontal flight. During each of the three general zones of the flight envelope of the air vehicle, the gyroscopic stabilization member provides gyroscopic stabilization about a pitch axis and a yaw axis which are perpendicular to each other and also perpendicular to a roll axis which, in one embodiment, comprises the longitudinal axis of the air vehicle and is coincident with the axis of rotation of the propeller.
The air vehicle of the present invention is more stable in operation due to the addition of the gyroscopic stabilization member. Further, directly linking the gyroscopic stabilization member to the drive shaft of a single propeller results in a stable, yet inexpensive, aircraft that is capable of both vertical and horizontal flight. The use of a ducted fan-type design in one embodiment of the invention provides a vehicle that is suitable for take-off and landing on confined surfaces without posing undo risk to operating personnel standing nearby. These and other objects and advantages of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings.